A water supply system, e.g. a municipal water system, typically comprises a main supply line fed from a source of water (water reservoir, well, lake, etc.) and pumping means for propelling the water through a network of pipes so it can reach various consumers downstream.
Typically, there are also provided various pressure regulating and control means along the pipe's network in order to monitor the water flow and to reduce pressure of water to such a level that will, on the one hand, ensure proper functioning of various systems which are pressure activated, e.g. irrigation systems valving means, etc. and, on the other hand, will not damage any end equipment of the consumers by excessive pressure, e.g. burst of pipes, damage of solar heaters, and other domestic equipment connected to the water network (dishwashers, washing machines, etc.). Excessive pressure may also be harmful for industrial facilities receiving water from the network.
Hereinafter in the specification and claims the term “pipe network” refers to the piping and installations extending from the water source to the consumers.
The consumers of a water supply system may be for example domestic consumers, industrial facilities, public and municipal facilities, agricultural consumers, etc., all of which being referred to herein in the specification and claims collectively as a “network of consumers”.
Among the network of consumers there is at least one consumer at a location where the measured pressure is lower than the pressure measured at the other consumer sites. Such a consumer may be for example a remote one whereby pressure loss occurs owing to flow through a long and branching pipeline (friction and head loss), or a consumer at an elevated location (high building or on a mountain) etc.
Hereinafter in the specification and claims, the one or more consumer at which lowest pressure is measured is referred to as a “monitored consumer” (also known as a “critical consumer”).
Water consumption in a municipal water supply system varies throughout the day. Increased consumption is typically measured at the morning hours (between about 6 and 9 a.m.) and again in the evening hours (between about 7 and 9 p.m.). However, these peaks are subject to changes, e.g. at weekends, upon setting of DST, season changes, major events such as an important sports match, etc.
It is the concern of the water supplying authority, for example a municipality or a water supplying company, that the monitored consumer receives water at a minimal pressure, say for example, about 2½ atmospheres so as to ensure proper functioning of various pressure activated equipment and to enjoy reasonable pressure at a domestic water facilities, e.g. taps, showers, etc. Increasing the pressure at the monitored consumer will necessarily entail a much more significant pressure increase at consumers upstream, even as much as harmful over pressure.
For one thing, over pressure demands more powerful pumping units and is more costly. Second, it requires a pipe network that can withstand such overpressure. Then there is a problem of over pressure which can cause damage to the consumers as already mentioned above.
Even more so, non-significant leaks in the pipe network, e.g. minor holes or poor connections of piping elements, become proportionally significant upon pressure increase and may be the reason for some significant loss of fresh water which goes astray. Reports show that rates of loss of fresh water by leaks reach as much as about 15 to 40% of a supplier's flow delivery.
A variety of water pressure and control systems are known. A basic arrangement comprises a pressure reducing valve (PRV) which functions to reduce pressure between an inlet and an outlet thereof, regardless of flow changes through the device or change of pressure upstream. Several such PRVs are typically fitted along a pipe network, e.g. at branchings to suburbs, adjacent major consuming facilities, buildings, etc.
A typical PRV comprises an inlet port being in flow communication with an outlet port via a flow passage governed by a pressure control chamber. When the pressure control chamber is pressurized, the flow passage is restricted to thereby restrict flow between the inlet and the outlet port so as to obtain essentially constant outlet pressure.
Pressure within the control chamber is governed by various flow control means which eventually serve for the purpose of controlling the water flow rate through the control chamber.
In accordance with one prior art embodiment there is provided a so-called hydraulic valve, wherein the pressure chamber is charged by a restriction orifice having a constant inlet flow rate Q1 connected upstream of the PRV and is discharged by a pilot valve having a set nominal outlet flow Q2 connected downstream of said PRV. When Q1 is greater than Q2 the pressure within the pressurized control chamber increases to thereby restrict (or close) the flow passage between the inlet port and the outlet port of the PRV to thereby restrict the outlet flow Qout of the PRV, entailing a corresponding drop in out let pressure Pout of the PRV.
In accordance with a different arrangement, rather than the restriction orifice and the pilot valve, there are provided solenoids (optionally proportional solenoids) connected to electric controllers, whereby water inlet flow Q1 and outlet flow Q2 are controlled to thereby govern pressure within the control chamber.
In accordance with still a different embodiment a bias chamber is fitted onto a plunger of the pilot valve for hydraulically activating an internal diaphragm of the pilot valve. Said bias chamber is connected to an upstream water supply whereby a plunger of the pilot valve is displaceable to restrict the outlet flow Q2 of the pilot valve.
Still another control system is concerned with fitting a bias chamber onto an adjusting member of a pilot valve supply whereby the adjusting member of the pilot valve is displaceable so as to restrict the outlet flow Q2 of the pilot valve.
In accordance with an embodiment of the above solution, there is provided a bias chamber integrally fitted with the pilot valve. Nevertheless, control solenoids are still required for restricting the inlet flow Q1 and the outlet flow Q2.
Each of the above control systems have at least one of several deficiencies and drawbacks as follows:                i. Malfunctioning of one or both the solenoids renders the PRV inactive. This may result in one of two undesired extreme positions, the first being complete cut-off of the water supply and the second being providing the consumers with a pressure which is equal to high pressure upstream (as the PRV does not fulfil its function) whereby the water supplier is exposed to malfunctioning liability owing to damages caused to consumers.        ii. Every recognizable pressure or flow change entails activation of the solenoids whereby an associated power source is rapidly exhausted;        iii. Increased openings/closing of the solenoids and valve components may render the system vulnerable to malfunction.        iv. Usage of solenoids requires filtration of the water at a high level (typically as much as microns). Thus increased maintenance is expected.        v. An important factor is the option to install the control system in retrofit. In most cases individual fittings and installations are required which render the installation not cost effective.        vi. At low flow rates the system enters a so called hunting state where the system is unsuccessful in reaching a steady state.        vii. The bias chamber is a sensitive element requiring fine adjustments and being susceptible to dirt.        viii. The systems does not offer any bypassing arrangements, whereby malfunctioning of such a system may result in that the consumer will receive excessively high pressure, which may cause damage.        
It is thus an objection of the present invention to provide a water supply control system capable of providing essentially desired pressure at the monitored consumer regardless changes in consumption, i.e. flow rate through the system. A water supply system in accordance with the invention provides for essentially constant pressure measured at the monitored consumer regardless of its location and head loss in the piping network and also regardless of sudden changes in consumption or periodic such changes.
In accordance with another aspect of the present invention there is provided a differential control valve useful in obtaining a constant flow rate in spite of pressure changes in the line by eliminating such pressure alterations.
Still a further object of the present invention is to provide a method for controlling pressure at a water supply system so as to provide desired pressure at a monitored consumer.